Hazardous weather is generally associated with convective weather cells. Convective weather cells can produce turbulence, high winds, lightning, hail, and other weather hazards. With the large amount of air traffic and rising fuel costs, pilots are interested in identifying convective cells (e.g., often hazardous weather) from non-convective cells (e.g., stratiform rain) so they do not unnecessarily avoid flight routes through non-hazardous weather.
Lightning is generally caused by an updraft of induced charges. Generally, cells that are producing lightning are turbulent and have the capacity to produce hail. Therefore, the presence of lightning in a particular area can be an indication of the presence of a convective cell or at least a potentially hazardous weather region.
Weather radar systems generally include an antenna, a receiver/transmitter circuit, a processor, and display. The processor is coupled between the display and the receiver/transmitter circuit. The receiver/transmitter circuit is coupled between the processor and the antenna. The processor provides transmit signals through the receiver/transmitter circuit to the antenna to transmit radar beams. The processor receives radar return signals derived from radar returns received by the antenna. The radar return signals are provided to the processor via the receiver/transmitter circuit.
Conventionally, pilots use weather radar systems to detect and avoid hazardous weather. The radar return signals are processed to provide graphical images to a radar display. The radar display is typically a color display providing graphical images in color to represent the severity of weather. Some aircraft weather radar systems also include other hazard detection systems such as a turbulence detection system. The turbulence detection system can provide indications of the presence of turbulence or other hazards. Conventional weather radar systems include those manufactured by Rockwell Collins, Inc., Honeywell International, Inc. and others.
Some aircraft also utilize lightning sensors or lightning detection systems. Conventional lightning detection systems or lightning sensors include automatic direction finding (ADF-like) equipment at radio frequency (RF) or by narrow band optical imaging systems. Lightning sensors can include a display for showing the presence of lightning strikes with respect to the position of the aircraft.
Generally, lightning sensors have the ability to detect a rough spatial location of lightning strikes at a relatively significant range. However, conventional lightning sensors do not have the ability to locate and identify convective weather cells with relative accuracy and precision. Heretofore, lightning detection systems have not been effectively utilized with aircraft weather radar systems.
Both lightning sensors and weather radar systems have regions in their weather search range that are more accurate then other regions. Generally, lightning sensors have the ability to detect lightning strikes at long range, but cannot locate the distance to such lightning striking with a relatively high degree of accuracy. High performance weather radar systems can detect weather at substantial ranges but at some ranges have difficulty in determining whether or not an illuminated weather cell is hazardous.
Weather radar systems that utilize spectral width methods to determine turbulence hazards are generally used at ranges less then forty nautical miles because these methods are not as accurate at ranges greater then forty nautical miles. High performance weather radar systems can also utilize vertical reflectivity (e.g., cloud height) as an indicator of cell hazardousness. However, weather radar systems utilizing hazard detection methods based upon vertical reflectivity are limited in accuracy at longer ranges because the smaller antenna diameter of these systems prevents more accurate estimations of storm height.
In addition, certain weather phenomena (such as not convective or convective and dissipating weather cells that have substantial returns) are indicated as hazardous weather even though they are not necessarily hazardous. When the weather radar system indicates hazardous weather in response to this weather phenomena, the weather radar system unnecessarily provides hazard warnings and behaves more like a simple rain gauge than a hazard detector.
Lightning sensors can detect lightning at ranges far in excess of a weather radar system's ability to ascertain the level of a weather hazard. However, lightning sensors and lightning detection systems are generally not provided on aircraft because of their inherent range inaccuracy even though they provide accurate bearing estimations. Further, lightning detection by lightning sensors is generally only spatially correlated with hail and turbulence at scale lengths comparable to or greater than a typical size of a convective weather cell. Therefore, a lightning sensor is most accurate at pointing to the bearing of a cell that is producing lightning, and is less accurate at producing a range estimate to a hazard and identifying an aircraft sized path of safe passage.
Thunderstorm cores are difficult to identify using a conventional on-board weather radar system because weather frontal systems include many cells at different stages of development. Typically, a thunderstorm that has decayed still produces significant returns with a radar because the radar only detected water droplets, but water droplets do not necessarily pose a hazard to the aircraft. Within many thunderstorms, a new thunderstorm can develop that cannot be detected by the radar because it is growing within or adjacent to the decaying cell and is therefore obscured by the decaying cell. Growing or developing thunderstorm cells are generally hazards to aircraft because they include an updraft core that has turbulence, hail, and/or lightning associated with it. Convective cells can grow at rates between 1000 and 6000 ft/min. Conventional radar systems may not operate quickly enough to immediately detect quickly growing cells.
Intracloud or cloud to cloud lightning can be a good indicator of growing thunderstorms and their core regions. Unfortunately, airborne lightning detectors provide poor location information on the lightning flash location. The azimuth error may be in excess of 5 degrees and the range error may be in excess of 20%.
Therefore, there is a need for a weather radar system that accurately combines an airborne radar with an airborne lightning detector and is capable of identifying where high rain rates are located (extent of thunderstorm) and where the thunderstorm cores producing aviation hazards are located. There is also a need for a weather radar system and method capable of predicting weather as an aircraft approaches the weather. There is further a need for a weather radar system and method capable of identifying and predicting soft spots, penetration points, or decaying regions within weather frontal lines to avoid long deviations around frontal lines. There is further still a need for a weather radar system and method capable of quickly detecting convective changes in cells.
It would be desirable to provide a system and/or method that provides one or more of these or other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments which fall within the scope of the appended claims, regardless of whether they accomplish one or more of the aforementioned needs.